This invention addresses the lifetime/lifespan that is seen in field emission devices, in particular those that employ carbon nanotubes as the active field emitters. Short lifetime in a field emission device is one of the chief obstacles that must be overcome for the device to be a viable contender in the marketplace. By applying sufficient potential to the anode (VA) of a field emission diode device, or to the gate electrode (VG) of a field emission triode device, an emission current will be caused to flow. As the emitters degrade, a greater potential must be applied to maintain a constant emission current. The rate of increase of this applied potential is a good indicator of the degradation rate of the emitters and what the lifespan of a particular device might be. From the rate of increase of the applied potential, an extrapolation can be made of how long it will take for the potential to reach the upper bound of what is possible to supply in a particular device. For applications such as field emission displays, it is desired that the lifespan of the device be at least 30,000 hours. A significant percentage of field emission devices, particularly nanotube-based devices, have been unable to demonstrate lifespans on this scale.
U.S. Pat. No. 6,888,294 discloses a field emission device which contains a nitrogen hydride reducing gas for preventing emissive material oxidation, particularly where molybdenum emitters are used. U.S. Pat. No. 6,722,936 discloses a field emission device where carbon field emitters are deposited on heated areas through introduction of hydrocarbons prior to evacuation of the device. WO 05/45871 discloses a field emission device comprising a coating layer formed on an outer surface of a carbon nanotube.
A need nevertheless remains for methods to enhance the lifespan of a field emission device, and for the improved devices resulting from the employment of such methods.